The invention relates to a method for monitoring the crane safety of a crane, as well as to a crane with a variable support base.
It is known to monitor crane safety by means of a crane control system during crane operation. Ensuring crane safety is based on complying with various safety criteria. Examples of possible safety criteria are the component strength of jib systems, hoist ropes, load hooks, slewing ring, luffing cylinder, mechanical connections, etc., on the one hand, and the stability of the crane, on the other hand. Criteria pertaining to the stability of the crane are, for example, the tilting of the crane in the load direction, the tilting of the crane in the direction opposite the load direction, wind speed, the planned upper carriage rotation angle, etc. For each one of these criteria, admissible limit values can be determined, which have to be monitored separately for compliance to ensure crane safety during the operation of the crane.
The monitoring process is carried out automatically by an implemented crane control system, in particular by the load moment device of the crane. Monitoring events can be displayed, and they can optionally lead to intervention in the crane movement.
During the manufacture and the verification of the crane, to begin with, so-called load charts are calculated for all the mentioned criteria, the chart entries of which define the maximum admissible bearing loads for concrete crane configurations.
As a rule, a crane is operated in a supported state, wherein the size of the support base is dependent on the extension state or deployment state of the rail spars or collapsible spars of the support device. If a symmetric support is impossible due to the installation site, EP 0 779 238 B1 proposes to reduce the entire supporting base to the smallest present deployed state or collapsed state. The disadvantage of this approach is that actually present bearing load is lost in large portions of the upper carriage rotation angle. In addition, in this embodiment, the position of the rail spars or collapsible spars is limited to predetermined concrete positions, since the operation of the crane is admissible only for a limited number of support positions.
EP 0 779 238 B1 proposes an alternative solution. This solution establishes individual rotation angle ranges for the upper carriage, and it indicates a uniform maximum bearing load for each range. This determined maximum bearing load in each case corresponds to the smallest bearing load admissible in the individual ranges. In this solution as well, due to the jump between the rotation angle ranges, actually present bearing load is lost.
An alternative approach is known from DE 20 2006 017 730 U1. The above-mentioned safety criteria are no longer monitored exclusively on the basis of previously calculated and stored load charts; instead, some of said criteria are also monitored individually in comparison to the values currently existing on the crane. As a result, a certain diversity in the monitoring of the crane is achieved; however, the maximum possible bearing load cannot be exhausted due to the recourse to individual load charts.
DE 10 2005 035 460 A1 proposes to extract, from the existing load charts, individual support points for certain crane states, and, on the basis of these support values, to determine the actually existing maximum bearing load by interpolation. Again, the determined admissible bearing load is affected by a certain amount of imprecision, which may lead to an appreciable loss of maximum bearing load.
The embodiment variants known from the prior art have in common that previously calculated load charts are always used. However, a variable crane configuration, in particular a variable support base, leads to an infinite number of possible crane configurations and corresponding load charts. It is desirable to be able to design the crane configuration as flexibly as possible, particularly at the site of use.
Known cranes are operated in such a manner that the parameters can be modified until the admissible bearing load corresponds to the actual bearing load or exceeds the latter. The crane control system is used to prevent moving the crane into an inadmissible range and it prohibits further crane movements that would lead to exceeding a limit. The admissible bearing load is determined in each instance on the basis of the stored load charts. However, if one deviates from the usual practice with previously calculated load charts, these necessary fixed limit values are missing, and it is not possible moreover to define fixed intervention limits and warning limits.
If this limit is nevertheless exceeded during crane operation, possibly owing to a change in weather conditions, then the crane is in the inadmissible operating range. In order to reduce the associated hazards, an intervention of the load moment device in the crane control system occurs, the results of which may include the complete blocking of all crane movements.
To date, a so-called key-operated switch has been provided, which allows the performance of crane movements without or with an only partially active load moment device. This function was useful for readying the crane for work, or also for moving it out of an inadmissible operational range, for example, when the load moment device has stopped a crane movement.
Now, if a key-operated switch is no longer incorporated, the crane movements can be carried out only if they occur in the admissible bearing load range. However, if the crane has been moved into an inadmissible range, then the load moment device interrupts the current crane movement and blocks all further crane movements.